Animal vocalizations in natural settings are invariably accompanied by an acoustic background with a complex statistical structure. We have previously demonstrated that neuronal responses in primary auditory cortex of halothane-anesthetized cats depend strongly on the natural background. Here, we study in detail the neuronal responses to the background sounds and their relationships to the responses to the foreground sounds. Natural bird chirps as well as modifications of these chirps were used. The chirps were decomposed into three components: the clean chirps, their echoes, and the background noise. The last two were weaker than the clean chirp by 13 and 29 dB on average respectively. The test stimuli consisted of the full natural stimulus, the three basic components, and their three pairwise combinations. When the level of the background components (echoes and background noise) presented alone was sufficiently loud to evoke neuronal activity, these background components had an unexpectedly strong effect on the responses of the neurons to the main bird chirp. In particular, the responses to the original chirps were more similar on average to the responses evoked by the two background components than to the responses evoked by the clean chirp...

A recent study evaluates auditory brainstem responses (ABRs) evoked by chirps of different durations (sweeping rates) [Elberling et al. (2010). J. Acoust. Soc. Am. 128, 215–223]. The study demonstrates that shorter chirps are most efficient at higher levels of stimulation whereas longer chirps are most efficient at lower levels. Mechanisms other than the traveling wave delay, in particular, upward spread of excitation and changes in cochlear-neural delay with level, are suggested to be responsible for these findings. As a consequence, delay models based on estimates of the traveling wave delay are insufficient for the design of chirp stimuli, and another delay model based on a direct approach is therefore proposed. The direct approach uses ABR-latencies from normal-hearing subjects in response to octave-band chirps over a wide range of levels. The octave-band chirps are constructed by decomposing a broad-band chirp, and constitute a subset of the chirp. The delay compensations of the proposed model are similar to those found in the previous experimental study, which thus verifies the results of the proposed model.

Auditory brainstem responses (ABRs) are recorded in ten normal-hearing adults (20 ears) in response to a standard 100 μs click and five chirps having different durations (sweeping rates). The chirps are constructed from five versions of a power function model of the cochlear-neural delay that is based on derived-band ABR latencies from N=81 normal-hearing adults [Elberling, C., and Don, M. (2008). J. Acoust. Soc. Am. 124, 3022–3037]. The click and the chirps have identical amplitude spectra and, in general, for each of the three stimulus levels 60, 40, and 20 dB nHL, the ABRs to the chirps are significantly larger than the ABRs to the click. However, the shorter chirps are the most efficient at higher levels of stimulation whereas the longer chirps are the most efficient at lower levels. It is suggested that two different mechanisms are responsible for these observed changes with stimulus level—(1) upward spread of excitation at higher levels, and (2) an increased change of the cochlear-neural delay with frequency at lower levels.

The frequency response and sensitivity of the ER-3A and ER-2 insert earphones are measured in the occluded-ear simulator using three ear canal extensions. Compared to the other two extensions, the DB 0370 (Brüel & Kjær), which is recommended by the international standards, introduces a significant resonance peak around 4500 Hz. The ER-3A has an amplitude response like a band-pass filter (1400 Hz, 6 dB/octave – 4000 Hz, −36 dB/octave), and a group delay with “ripples” of up to ±0.5 ms, while the ER-2 has an amplitude response, and a group delay which are flat and smooth up to above 10000 Hz. Both earphones are used to record auditory brainstem responses, ABRs, from 22 normal-hearing ears in response to two chirps and a click at levels from 20 to 80 dB nHL. While the click-ABRs are slightly larger for ER-2 than for ER-3A, the chirp-ABRs are much larger for ER-2 than for ER-3A at levels below 60 dB nHL. With a simulated amplitude response of the ER-3A and the smooth group delay of the ER-2 it is shown that the increased chirp-ABR amplitude with the ER-2 is caused by its broader amplitude response and not by its smoother group delay.

This paper describes the estimation of hearing thresholds in normal-hearing and hearing-impaired subjects on the basis of multiple-frequency auditory steady-state responses (ASSRs). The ASSR was measured using two new techniques: (i) adaptive stimulus patterns and (ii) narrow-band chirp stimuli. ASSR thresholds in 16 normal-hearing and 16 hearing-impaired adults were obtained simultaneously at both ears at 500, 1000, 2000, and 4000 Hz, using a multiple-frequency stimulus built up of four one-octave-wide narrow-band chirps with a repetition rate of 40 Hz. A statistical test in the frequency domain was used to detect the response. The recording of the steady-state responses was controlled in eight independent recording channels with an adaptive, semiautomatic algorithm. The average differences between the behavioural hearing thresholds and the ASSR threshold estimate were 10, 8, 13, and 15 dB for test frequencies of 500, 1000, 2000, and 4000 Hz, respectively. The average overall test duration of 18.6 minutes for the threshold estimations at the four frequencies and both ears demonstrates the benefit of an adaptive recording algorithm and the efficiency of optimised narrow-band chirp stimuli.

Recently it has been demonstrated that auditory brainstem responses, ABRs, to chirps are larger with the ER-2 than with the ER-3A insert earphone due to differences between the corresponding amplitude-frequency responses. Therefore a modified chirp, which equalizes the amplitude-frequency response of the ER-3A, is constructed and subsequently compared to the unmodified chirp. ABRs are recorded from 20 normal-hearing subjects in response to the two chirps delivered by the ER-3A earphone at a wide range of levels. The results confirm that the modified chirp generates significantly larger ABRs than the unmodified chirp at levels below 60 dB nHL.

We describe a new approach to analyze chirp syllables of free-tailed bats from two regions of Texas in which they are predominant: Austin and College Station. Our goal is to characterize any systematic regional differences in the mating chirps and assess whether individual bats have signature chirps. The data are analyzed by modeling spectrograms of the chirps as responses in a Bayesian functional mixed model. Given the variable chirp lengths, we compute the spectrograms on a relative time scale interpretable as the relative chirp position, using a variable window overlap based on chirp length. We use 2D wavelet transforms to capture correlation within the spectrogram in our modeling and obtain adaptive regularization of the estimates and inference for the regions-specific spectrograms. Our model includes random effect spectrograms at the bat level to account for correlation among chirps from the same bat, and to assess relative variability in chirp spectrograms within and between bats. The modeling of spectrograms using functional mixed models is a general approach for the analysis of replicated nonstationary time series, such as our acoustical signals, to relate aspects of the signals to various predictors, while accounting for between-signal structure. This can be done on raw spectrograms when all signals are of the same length...

Males of the bushcricket Mecopoda elongata synchronise or alternate their chirps with their neighbours in an aggregation. Since synchrony is imperfect, leader and follower chirps are established in song interactions; females prefer leader chirps in phonotactic trials. Using playback experiments and simulations of song oscillator interactions, we investigate the mechanisms that result in synchrony and alternation, and the probability for the leader role in synchrony. A major predictor for the leader role of a male is its intrinsic chirp period, which varies in a population from 1.6 to 2.3 s. Faster singing males establish the leader role more often than males with longer chirp periods. The phase-response curve (PRC) of the song oscillators differs to other rhythmically calling or flashing insects, in that only the disturbed cycle is influenced in duration by a stimulus. This results in sustained leader or follower chirps of one male, when the intrinsic chirp periods of two males differ by 150 ms or more. By contrast, the individual shape of the male’s PRC has only little influence on the outcome of chirp interactions. The consequences of these findings for the evolution of synchrony in this species are discussed.

Sensory stimuli such as sound or light enter the nervous system through receptor cells. Only the information that is encoded in receptor cells can be further processed, perceived and eventually influence behaviour. As in other parts of the nervous system, information is not taken up by a single receptor but by many receptor neurons that form a population. Individual neurons in a population often differ slightly in the way they encode a stimulus. The population is then said to exhibit heterogeneity. This thesis deals with the encoding of sensory signals in heterogeneous populations of electroreceptor neurons. The investigation is based on the example of the encoding of communication signals in electroreceptor populations in the weakly-electric fish Apteronotus leptorhynchus.
Weakly-electric fish generate an electric organ discharge (EOD) and use perturbations and modulations of it to navigate and communicate. A. leptorhynchus generates a quasisinusoidal EOD with a frequency that is very stable under baseline conditions. Frequency modulations are used by the fish to communicate. This thesis focuses on chirps, which consist of transient (on the order of milliseconds) increases in EOD frequency. Chirps occur on top of beats, sinusoidal amplitude modulations (AM) formed by the superposition of the EODs of two communicating fish. AMs are sensed by P-type electroreceptors that are distributed over the whole body of the fish. The frequency of the beat is determined by the difference between the EOD frequencies of the two fish.
In A. leptorhynchus beat frequencies range from a couple up to a couple of hundred hertz. Since the EOD frequency of each fish depends on its gender...

Conference Paper; We study the problem of locating in space and over time a network pathâ s tight link, that is the link with the least available bandwidth on the path. Tight link localization benefits network-aware applications, provides insight into the causes of network congestion and ways to circumvent it, and aids network operations. We present STAB, a light-weight probing tool to locate tight links. STAB combines the probing concepts of self-induced congestion, tailgating, and packet chirps in a novel fashion. We demonstrate its capabilities through experiments on the Internet and verify our results using router MRTG data.

Although female mammal vocal behaviour is known to advertise fertility, to date, no non-human mammal study has shown that the acoustic structure of female calls varies significantly around their fertile period. Here, we used a combination of hormone measurements and acoustic analyses to determine whether female giant panda chirps have the potential to signal the caller's precise oestrous stage (fertile versus pre-fertile). We then used playback experiments to examine the response of male giant pandas to female chirps produced during fertile versus pre-fertile phases of the caller's reproductive cycle. Our results show that the acoustic structure of female giant panda chirps differs between fertile and pre-fertile callers and that male giant pandas can perceive differences in female chirps that allow them to determine the exact timing of the female's fertile phase. These findings indicate that male giant pandas could use vocal cues to preferentially associate and copulate with females at the optimum time for insemination and reveal the likely importance of female vocal signals for coordinating reproductive efforts in this critically endangered species.

It has been shown recently that chirp-evoked auditory brainstem responses (ABRs) show better performance than click stimulations, especially at low intensity levels. In this paper we present the development, test, and evaluation of a series of notched-noise embedded frequency specific chirps. ABRs were collected in healthy young control subjects using the developed stimuli. Results of the analysis of the corresponding ABRs using a time-scale phase synchronization stability (PSS) measure are also reported. The resultant wave V amplitude and latency measures showed a similar behavior as for values reported in literature. The PSS of frequency specific chirp-evoked ABRs reflected the presence of the wave V for all stimulation intensities. The scales that resulted in higher PSS are in line with previous findings, where ABRs evoked by broadband chirps were analyzed, and which stated that low frequency channels are better for the recognition and analysis of chirp-evoked ABRs. We conclude that the development and test of the series of notched-noise embedded frequency specific chirps allowed the assessment of frequency specific ABRs, showing an identifiable wave V for different intensity levels. Future work may include the development of a faster automatic recognition scheme for these frequency specific ABRs.

The searches of impulsive gravitational waves (GW) in the data of the
ground-based interferometers focus essentially on two types of waveforms: short
unmodeled bursts and chirps from inspiralling compact binaries. There is room
for other types of searches based on different models. Our objective is to fill
this gap. More specifically, we are interested in GW chirps with an arbitrary
phase/frequency vs. time evolution. These unmodeled GW chirps may be considered
as the generic signature of orbiting/spinning sources. We expect quasi-periodic
nature of the waveform to be preserved independent of the physics which governs
the source motion. Several methods have been introduced to address the
detection of unmodeled chirps using the data of a single detector. Those
include the best chirplet chain (BCC) algorithm introduced by the authors. In
the next years, several detectors will be in operation. The joint coherent
analysis of GW by multiple detectors can improve the sight horizon, the
estimation of the source location and the wave polarization angles. Here, we
extend the BCC search to the multiple detector case. The method amounts to
searching for salient paths in the combined time-frequency representation of
two synthetic streams. The latter are time-series which combine the data from
each detector linearly in such a way that all the GW signatures received are
added constructively. We give a proof of principle for the full sky blind
search in a simplified situation which shows that the joint estimation of the
source sky location and chirp frequency is possible.; Comment: 22 pages...

We present a novel technique for producing pulses of laser light whose
frequency is arbitrarily chirped. The output from a diode laser is sent through
a fiber-optical delay line containing a fiber-based electro-optical phase
modulator. Upon emerging from the fiber, the phase-modulated pulse is used to
injection-lock the laser and the process is repeated. Large phase modulations
are realized by multiple passes through the loop while the high optical power
is maintained by self-injection-locking after each pass. Arbitrary chirps are
produced by driving the modulator with an arbitrary waveform generator.

The general problem of computing the false-alarm rate vs. detection-threshold
relationship for a bank of correlators is addressed, in the context of
maximum-likelihood detection of gravitational waves, with specific reference to
chirps from coalescing binary systems. Accurate (lower-bound) approximants for
the cumulative distribution of the whole-bank supremum are deduced from a class
of Bonferroni-type inequalities. The asymptotic properties of the cumulative
distribution are obtained, in the limit where the number of correlators goes to
infinity. The validity of numerical simulations made on small-size banks is
extended to banks of any size, via a gaussian-correlation inequality. The
result is used to estimate the optimum template density, yielding the best
tradeoff between computational cost and detection efficiency, in terms of
undetected potentially observable sources at a prescribed false-alarm level,
for the simplest case of Newtonian chirps.; Comment: submitted to Phys. Rev. D

We study the fractal oscillatority of a class of real $C^1$ functions
$x=x(t)$ near $t=\infty$. It is measured by oscillatory and phase dimensions,
defined as box dimensions of the graph of $X(\tau)=x(\frac{1}{\tau})$ near
$\tau=0$ and the trajectory $(x,\dot{x})$ in $\mathbb{R}^2$, respectively,
assuming that $(x,\dot{x})$ is a spiral converging to the origin. The
relationship between these two dimensions has been established for a class of
oscillatory functions using formulas for box dimensions of graphs of chirps and
nonrectifiable wavy spirals, introduced in this paper. Wavy spirals are a
specific type of spirals, given in polar coordinates by $r=f(\varphi)$,
converging to the origin in non-monotone way as a function of $\varphi$. They
emerged in our study of phase portraits associated to solutions of Bessel
equations. Also, the rectifiable chirps and spirals have been studied.

The list of putative sources of gravitational waves possibly detected by the
ongoing worldwide network of large scale interferometers has been continuously
growing in the last years. For some of them, the detection is made difficult by
the lack of a complete information about the expected signal. We concentrate on
the case where the expected GW is a quasi-periodic frequency modulated signal
i.e., a chirp. In this article, we address the question of detecting an a
priori unknown GW chirp. We introduce a general chirp model and claim that it
includes all physically realistic GW chirps. We produce a finite grid of
template waveforms which samples the resulting set of possible chirps. If we
follow the classical approach (used for the detection of inspiralling binary
chirps, for instance), we would build a bank of quadrature matched filters
comparing the data to each of the templates of this grid. The detection would
then be achieved by thresholding the output, the maximum giving the individual
which best fits the data. In the present case, this exhaustive search is not
tractable because of the very large number of templates in the grid. We show
that the exhaustive search can be reformulated (using approximations) as a
pattern search in the time-frequency plane. This motivates an approximate but
feasible alternative solution which is clearly linked to the optimal one.
[abridged version of the abstract]; Comment: 23 pages...

Pulse compression is often practiced in ultrasound Non Destructive Testing
(NDT) systems using chirps. However, chirps are inadequate for setups where
multiple probes need to operate concurrently in Multiple Input Multiple Output
(MIMO) arrangements. Conversely, many coded excitation systems designed for
MIMO miss some chirp advantages (constant envelope excitation, easiness of
bandwidth control, etc.) and may not be easily implemented on hardware
originally conceived for chirp excitations. Here, we propose a system based on
random-FM excitations, capable of enabling MIMO with minimal changes with
respect to a chirp-based setup. Following recent results, we show that
random-FM excitations retain many advantages of chirps and provide the ability
to frequency-shape the excitations matching the transducers features.; Comment: 4 pages, 4 figures. Post-print from conference proceedings. Note that
paper in conference proceedings at http://dx.doi.org/10.1109/ULTSYM.2012.0117
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